A light emitting apparatus in which a semiconductor light emitting element and a phosphor are combined attracts attention as the next-generation light emitting apparatus whose low power consumption, reduced size, high luminance, and wide range color reproducibility are desired, and has been actively researched and developed. Generally, primary light emitted from the semiconductor light emitting element is light which has a range of a near-ultraviolet region to a blue region, and has a wavelength of 380 to 490 nm, for example. Light emitting apparatuses which use various phosphors suitable for the use purpose have also been proposed.
A light emitting apparatus used as, for example, an illumination apparatus has been also variously developed, and various technologies for improving output performance of such a light emitting apparatus are examined. Generally, a phosphor which has high visibility and has the main emission peak in a region for the yellow color which is a complementary color of the blue color is used for improving output performance of a light emitting apparatus. In a light emitting apparatus which can be used for general lighting equipment, it is important to have high color rendering properties (“having high color rendering properties” basically means that an average color rendering index Ra is equal to or greater than 80) and to improve the output performance.
The average color rendering index Ra is generally used as an index indicating the color rendering properties and is an indicator for evaluating whether or not test colors (R1 to R8) are caused to naturally look. In the light emitting apparatus which can be used for general lighting equipment, it is possible to cause the test color to naturally look, that is, it is important to increase the average color rendering index Ra.
As a light emitting apparatus which uses a light emitting diode (LED) light source, there is a light emitting apparatus which uses a blue LED having a peak in a wavelength region of 440 to 460 nm, and a green phosphor and a red phosphor. However, an emission spectrum of the light emitting apparatus has a sharp peak in the wavelength region of 440 to 460 nm, which is a blue region. Thus, a reflection component of the blue color is too strong. In this case, it may not be possible to reproduce a color of an irradiation target that reflects light in the wavelength region of 440 to 460 nm.
In a light emitting apparatus used for, for example, sales of products have a demand to ensure brightness and a demand for reproducibility of the color of an irradiation target. In particular, white, black, navy, and red are colors which are used most frequently in various types of commodities in industries including a clothing industry. Thus, it is important to faithfully reproduce these colors. Accordingly, in a case of such a light emitting apparatus, it is important to improve reproducibility of the white, black, navy, and red colors in addition to the average color rendering index Ra. The average color rendering index Ra is an indicator for evaluating whether the test colors (R1 to R8) are caused to naturally look, and does not indicate reproducibility of the white, red, navy, and black colors which are not included in the test colors. Regarding the red color, a special color rendering index R9 is generally used as an indicator. However, the white, black, and navy colors are not included in the test colors and do not have an evaluation index which is general and has quantitative properties.
PTL 1 (Japanese Patent No. 4072632) discloses a light emitting apparatus as follows, as a light emitting apparatus which vividly develops the red color. The light emitting apparatus includes a light emitting element and a sialon-based phosphor. The light emitting element has a light emission wavelength in a range of 360 nm to 550 nm. The sialon-based phosphor is configured with powder in which α-sialon which has a structure in which a Ca position in Ca-α-sialon represented by a formula of (Cax, Euy) (Si, Al)12(O, N)16 is partially substituted with Eu is 40 mass % to 90 mass %, β-sialon is 5 mass % to 40 mass %, and silicon nitride which is not caused to react is 5 mass % to 30 mass %. A portion of light of the light emitting element has a wavelength converted by the phosphor and then is emitted.